PIK3CA kinase domain mutation identifies a subgroup of stage III colon cancer patients with poor prognosis

Abstract

PIK3CA mutations in the helical domain (in exon 9) and in the kinase domain (exon 20) cause tumor formation by different means. We aimed to determine the effects of each of these mutations on survival of colon carcinoma patients. A large cohort of 685 colon carcinoma patients was tested for PIK3CA mutations in exons 9 and 20 by single nucleotide primer extension (N = 428) or by real time PCR (N = 257). PIK3CA mutation rate was 13%. 66 of 83 (79.5%) were in exon 9 and 17 of 83 (20.5%) in exon 20. In survival analysis, PIK3CA mutations in exon 9 and 20 had different effects on patient outcome. The PIK3CA exon 20 mutation conferred a poorer disease free survival compared to patients with wild type alleles and exon 9 mutations (Log rank p = 0.04 and p = 0.03 respectively) and cancer specific survival (Log rank p = 0.03 and p = 0.056 respectively) in stage III patients. In stage I and II this negative effect on outcome was not seen. PIK3CA mutation in exon 20 is a negative prognostic factor in stage III colon cancer patients. Moreover, this negative effect is not present in stage I and II patients.